console.log("hello,world!")
let age=18;
age=19;
const pi=3.14;
let userName="yuyu"
let email="1640918664@qq.com"
let fristName = "yu"
let lastName = "yu"
let fullName = fristName + " " + lastName
console.log("userName:",userName)
console.log("age:",age)
console.log("pi:",pi)
console.log("email:",email)
console.log(fullName)
console.log(fullName[1])
console.log(fullName.length)
console.log(fullName.toUpperCase())
let result = fullName.toLowerCase()
console.log(result)
let index = email.indexOf("@")
console.log(index)
let res = email.slice(0, 5)
console.log(res)
